Peripheral units that are used upon being connected to a personal computer or the like include a multifunction apparatus so adapted that any of multiple types of devices can be attached thereto selectively, with the apparatus executing a function that differs depending upon the type of device attached.
A well-known example of such a multifunction apparatus is a printer so adapted that a printhead or scanner unit can be selectively mounted on a carriage. The printer exercises control so as to execute a printing operation if the printhead has been mounted and an operation for reading a document image if the scanner head has been mounted.
A printer of the kind mentioned above is designed so as to identify the attached device by reading the device ID. Primarily, either of the two methods described below may be adopted as a method of reading an ID.
According to the first method, signal lines the number of which corresponds to the number of bits needed to discriminate an ID are provided, these signal lines are clamped to an ID value decided uniquely on the device side, and the ID is read from a controller in the apparatus. According to the second method, one data line and one synchronizing clock line are provided and the ID value is read out serially.
In the example of the prior art described above, however, the electrical connection between the device and the apparatus can become faulty if the user has not attached the device correctly or if the contacting parts become contaminated with dust or the like. This can result in the ID value being read incorrectly.
If the ID value is read incorrectly, the device will not be controlled properly and will not operate in the manner intended by the user. In addition, an inappropriate value can damage the attached device or the apparatus itself.
In order to avoid the problem mentioned above, there has been proposed an arrangement in which the connection between the multifunction apparatus and devices can be confirmed by providing the ID values of all devices that can be attached to the multifunction apparatus with header bits. However, this makes it necessary to add on circuits to all attached devices, thereby increasing the size and raising the cost of each device.